Monday, February 6, 2012

Quantum computing not like Martian trip

I became interested in quantum computing because of a simple trilemma: either (i) the Extended Church-Turing Thesis is false, (ii) quantum mechanics is false, or (iii) factoring is in classical polynomial time. As I put it in my dissertation, all three possibilities seem like wild, crackpot speculations, but at least one of them is true! The question of which will remain until it’s answered. ...

Yeah, alright. So I ought to amend (ii) from “quantum mechanics is false” to “current low-energy physical theories are wrong.”

No, if you accept quantum mechanics, the burden is on you to explain why a computer couldn’t be built that takes advantage of the phenomena of superposition, interference, and entanglement that have been the entire core of quantum mechanics, verified over and over, since 1926.

Believing quantum mechanics but not accepting the possibility of QC is somewhat like believing Newtonian physics but not accepting the possibility of humans traveling to Mars.

I accept quantum mechanics, but not quantum computing. It is just not true that quantum computing follows from the quantum mechanics of 1926. I guess Aaronson tried to show that in his papers cited below and failed. So he claims that somehow the burden is on someone else to show the opposite.

The Mars analogy is ridiculous. The feasibility of a Mars trip is an easy extrapolation from the Moon trip. But there is no demonstrated feasibility of quantum computing.

Scott Aaronson replies:

Sure, it’s easy to understand the impossibility of quantum computing, in exactly the same way it’s easy to understand how the earth can be resting on a giant turtle. The key is not to ask what the turtle’s standing on, and likewise, not to ask what the flaw is in our current understanding of quantum mechanics that makes QC impossible. All sorts of scientific problems can be quickly cleared up this way, once we learn to stop asking annoying followup questions and embrace doofosity!

The problem with quantum computing is that it does not follow from any established scientific theory, there is no observational evidence for it, and it leads to implausible outcomes. There are a lot of such speculative concepts in physics, and we ordinarily reject them. Examples are time travel, Maxwell's demon, tachyons, and wormholes. Quantum computing is like the giant turtle, and the burden on its proponents should be to show some good reason for believing in such a far-fetched concept.